Digital cameras have come a long way since their introduction a few decades ago. From bulky devices to today’s wafer-thin smartphones, digital cameras allow us to capture memories with just a click. At the heart of every digital camera lies an image sensor that converts light into digital data. One key component of modern image sensors is the shutter – but its design and function have evolved drastically over the years.
CCD vs CMOS Sensors
In the early days of digital photography, most cameras used charge-coupled device (CCD) sensors. These relied on mechanically operated shutters to control light exposure. When the shutter button was pressed, a physical curtain would open to expose the sensor to light before closing once the exposure was complete. While effective, mechanical shutters took up space and moving parts increased the risk of wear and tear.
The flip side was complementary metal-oxide-semiconductor (CMOS) sensors. These used on-chip electronic Shutter Image Sensor instead of physical mechanisms. By controlling individual photodiodes on the sensor electronically, CMOS cameras could start and stop exposures without any moving parts. This made them considerably smaller, thinner, and more reliable than CCD cameras. However, early CMOS sensors suffered from noise and lower image quality compared to CCD.
The Global Shutter Breakthrough
Initially, all CMOS sensors had a rolling shutter function where the entire sensor was not exposed simultaneously. This meant the top part of frames would be exposed fractions of a second before the bottom during fast motions, leading to skewed images. A major breakthrough came in the late 2000s with the invention of the global shutter. Now, every photosite on the sensor could be electronically shuttered at the exact same moment for a true instant exposure across the entire frame. This solved motion skewing issues and made CMOS sensors viable for applications like machine vision.
Hardware on Chips
Modern smartphone cameras almost exclusively use miniature CMOS image sensors with global shutters built directly into the silicon. With no need for bulky mechanical parts, sensor resolutions could increase while footprints shrank drastically. Sensor vendors also started integrating advanced hardware features directly onto the chip. Dedicated pixels were assigned for functions like phase detection autofocus while on-sensor analog-to-digital converters aided faster readouts. Global electronic shuttering and on-chip hardware brought CMOS performance at par with CCDs, resulting in its dominance across most applications today.
Software Shutter Control
Going beyond hardware, software also plays a key role in optimizing shutters. Rolling shutter artifacts, though reduced, can still appear when shooting very fast scenes on global shutter sensors. Most flagship cameras and smartphones address this using hardware synchronization and advanced software algorithms. By synchronizing internal clocks and precisely controlling electronic shutters, artifacts are further minimized without the need for incurring lags.
Computational photography techniques expand shutter capabilities in new ways too. HDR and multi-frame imaging uses variable shutter speeds across sequential exposures before merging the data. Learning algorithms also help simulate different shutter effects from a single capture. While mechanical shutters will always remain in pro DSLRs for specialized needs, software innovations ensures electronic shutters keep pace with evolving photography styles.
New Technologies on the Horizon
With global shutters becoming mainstream, researchers are exploring futuristic variants as well. One example is the global reset shutter which simultaneously resets all pixels before exposing them. This simplifies sensor circuitry while maintaining excellent image quality. 3D stacked sensors are another area of active research. By placing pixel arrays atop supporting logic dies, vertical space can be optimized for increasingly thin sized pixels. This pushes resolution and low light abilities to new heights.
Multi-aperture systems borrowing from computational photography can also reinvent shutters. Rather than exposing a traditional large format sensor sequentially, light could strike multiple smaller sensors simultaneously from different directions using exotic lens arrays. Software would then merge the data into expansive resolution composite shots. While difficult to implement, such ideas exhibit shutter potentials beyond conventional designs.
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1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it
